Scroll devices are well known in the field of vacuum pumps and compressors. In a scroll device, a movable spiral blade orbits with respect to a fixed spiral blade within a housing. The movable spiral blade is connected to an eccentric drive mechanism. The configuration of the scroll blades and their relative motion traps one or more volumes or “pockets” of a fluid between the blades and moves the fluid through the device. Most applications apply rotary power to pump a fluid through the device. Oil-lubricated scroll devices are widely used as refrigerant compressors. Other applications include expanders, which operate in reverse from a compressor, and vacuum pumps. Scroll pumps have not been widely adopted for use as vacuum pumps, mainly because the cost of manufacturing a scroll pump is significantly higher than a comparably-sized, oil-lubricated vane pump. Dry scroll pumps have been used in applications where oil contamination is unacceptable.
A scroll pump includes stationary and orbiting scroll elements, and a drive mechanism. The stationary and orbiting scroll elements each include a scroll plate and a spiral scroll blade extending from the scroll plate. The scroll blades are intermeshed together to define interblade pockets. The drive mechanism produces orbiting motion of the orbiting scroll element relative to the stationary scroll element so as to cause the interblade pockets to move toward the pump outlet.
Various scroll pump designs have been proposed in the prior art to increase performance and to reduce pump size. A two stage scroll pump is disclosed in U.S. Pat. No. 5,616,015, issued Apr. 1, 1997 to Liepert. U.S. Pat. No. 4,650,405, issued Mar. 17, 1987 to Iwanami et al., discloses a scroll pump with axially-spaced pumping chambers in series. A double-sided first stage feeds a single-sided second stage. A scroll compressor having two stages on opposite sides of an orbiting plate is disclosed in U.S. Pat. No. 5,304,047, issued Apr. 19, 1994 to Shibamoto. A single-sided scroll compressor having scroll blades with portions of different axial heights is disclosed in U.S. Pat. No. 4,477,238, issued Oct. 16, 1984 to Terauchi. A multi-stage, single-sided scroll compressor is disclosed in U.S. Pat. No. 6,050,792, issued Apr. 18, 2000 to Shaffer.
The prior art scroll pump designs have not been entirely satisfactory with respect to both performance and physical size. Accordingly, there is a need for improved scroll-type vacuum pumping apparatus.